Construction of N, P Co-Doped Carbon Frames Anchored with Fe Single Atoms and Fe₂ P Nanoparticles as a Robust Coupling Catalyst for Electrocatalytic Oxygen Reduction

A coupling catalyst of highly dispersed N, P co-doped carbon frames (NPCFs) anchored with Fe single atoms (SAs) and Fe₂ P nanoparticles (NPs) is synthesized by a novel in situ doping-adsorption-phosphatization strategy for the electrocatalytic oxygen reduction reaction (ORR). The optimized Fe SAs-Fe₂ P NPs/NPCFs-2.5 catalyst shows a superior ORR activity and stability in 0.5 m H₂ SO₄ and 0.1 m KOH, respectively. Theoretical calculations reveal a synergistic effect, in that the existence of Fe₂ P weakens the adsorption of ORR intermediates on active sites and lowers the reaction free energy. The doped P atoms with a strong electron-donating ability elevate the energy level of Fe-3d orbitals and facilitate the adsorption of O₂ . The active Fe atoms exist in a low oxidation state and are less positively charged, and they serve as an electron reservoir capable of donating and releasing electrons, thus improving the ORR activity. Operando and in situ characterization results indicate that the atomically dispersed FeN₄ /FeP coupled active centers in the Fe SAs-Fe₂ P NPs/NPCFs-2.5 catalyst are characteristic of the different catalytic mechanisms in acidic and alkaline media. This work proposes a novel idea for constructing coupling catalysts with atomic-level precision and provides a strong reference for the development of high-efficiency ORR electrocatalysts for practical application.